And would a racing thermostat, like Moshimoto's ($70) provide any HP gains? I live in Texas...

 

Silicone coolant hoses and thermostat will give you piece of mind-but no perfromance gains. If you are into endurance racing-then sure, your coolant temp will be more stable.
I really cannot tell if original hoses are going to rot quicker in Texas climate. If you're noticing cracks and "rough" feel-like when rubber dries out, I would definitely replace them.
I still have original ones.